ArcGIS Pro 3.4 API Reference Guide
ArcGIS.Core.Geometry Namespace / EllipticArcSegment Class / StartAngle Property
Example Version

StartAngle Property (EllipticArcSegment)
Gets the start angle in radians.
Syntax
public double StartAngle {get;}

Property Value

A double representing the start angle.
Remarks
The start angle is the angle of the line defined by the CenterPoint and the Segment.StartPoint. If RotationAngle != 0, then the start angle is relative to the rotated SemiMajorAxis rather than the X-axis. The start angle is is measured in radians and is always between -PI and +PI.
Example
Elliptic Arc Properties
// retrieve the curve's control points
EllipticArcSegment arc = EllipticArcBuilderEx.CreateEllipticArcSegment(arcSegment);
MapPoint startPt = arc.StartPoint;
MapPoint endPt = arc.EndPoint;
Coordinate2D centerPt = arc.CenterPoint;
bool isCircular = arc.IsCircular;
bool isMinor = arc.IsMinor;
bool isCounterClockwise = arc.IsCounterClockwise;
bool isCurve = arc.IsCurve;
double len = arc.Length;
double ratio = arc.MinorMajorRatio;

double semiMajorAxis, semiMinorAxis;
// get the axes
arc.GetAxes(out semiMajorAxis, out semiMinorAxis);
// or use the properties
// semiMajorAxis = arc.SemiMajorAxis;
// semiMinorAxis = arc.SemiMinorAxis;

double startAngle, centralAngle, rotationAngle;
// or use QueryCoords to get complete information
arc.QueryCoords(out centerPt, out startAngle, out centralAngle, out rotationAngle, out semiMajorAxis, out semiMinorAxis);

// use properties to get angle information
//double endAngle = arc.EndAngle;
//centralAngle = arc.CentralAngle;
//rotationAngle = arc.RotationAngle;
//startAngle = arc.StartAngle;
Requirements

Target Platforms: Windows 11, Windows 10

ArcGIS Pro version: 3 or higher.
See Also